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Restricted airflow reduces sensable and latent heat removal. The compressor load goes down, as does the blower load (slightly) and the system does use fewer watts, so less power is being used. However when the system operates below is't 100% design point, the efficiency of the system goes down, fewer BTUs but BUT/KW goes up somewhat. The loss of efficiency is greater with a piston expansion valve than a TXV.

One fact to remember is that any AC induction motor has its maximum efficiency at 100% load. As the load on the motor drops, efficiency drops as well. This is true for both the compressor and blower motor. This is one way a VF blower helps SEER since the loss of efficiency in a VF motor is lower since the speed is reduced to match the demand.

The amp draw of the blower fan is LESS with a dirty filter? Seems more sensible to me that the fan would work harder to pull the air through the more restrictive filter. Kinda like towing with your truck give you worse mileage...

Originally posted by scruit The amp draw of the blower fan is LESS with a dirty filter? Seems more sensible to me that the fan would work harder to pull the air through the more restrictive filter. Kinda like towing with your truck give you worse mileage...

Test it and you'll see with a PSC motor,static up,wattage/amps down.VS static up,wattage /amps up.

Originally posted by coggin air How do you loose efficiency of ac with dirty filter?

If your filter is dirty it would make your blower motor pull less amperage. If your filter is dirty your pressures will be lower, will it loose efficiency because it doesn't have the same cooling capacity with a dirty filter?

Well, if you read the side of the filter. It tells you to change every 30 days. There is a reason they say to do this.

If you do not do this, the HVAC man may be upset while you stand there with a stupid look on your face saying "Oh, I didn't know that filters had to be changed".

So you schedule your now pluged air handler to be cleaned after you get the filter on your car changed. You cigarettes have filters, your sunglasses are filters, your water is filtered, your coffee (the sweet nectar of life itself) is filtered through that little paper filter. Now, would you wait until your cars engine siezed, smoke Camels, go blind, drink contaminated water or nasty coffee before changing those filters?

I don't care what you do to yourself, just don't piss off the HVAC man or mess with my coffee..

Happiness is the only good. The time to be happy is now. The place to be happy is here. The way to be happy is to make others so.
-Robert Green Ingersoll

quote:
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Originally posted by scruit
The amp draw of the blower fan is LESS with a dirty filter? Seems more sensible to me that the fan would work harder to pull the air through the more restrictive filter. Kinda like towing with your truck give you worse mileage...
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Test it and you'll see with a PSC motor,static up,wattage/amps down.VS static up,wattage /amps up.
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I did the Dash Test as described above a few weeks ago. Then I went to work where we use Blowers from freight damaged units as fans in the shop.
I told my boss to block the discharge of the blower and it will
1: increase the cfm
2: reduce the current draw

His responce was "What, do you think you know more than --so & so--(commercial tech) ---if that were true he would have told us to do that a long time ago-----

so that nite when they were all gone I took a 8" piece of 20 ga ad blocked the discharge

when I came in the next afternoon every blower in the shop had the discharge blocked like the one I did..

Well, if you read the side of the filter. It tells you to change every 30 days. There is a reason they say to do this.

If you do not do this, the HVAC man may be upset while you stand there with a stupid look on your face saying "Oh, I didn't know that filters had to be changed".

So you schedule your now pluged air handler to be cleaned after you get the filter on your car changed. You cigarettes have filters, your sunglasses are filters, your water is filtered, your coffee (the sweet nectar of life itself) is filtered through that little paper filter. Now, would you wait until your cars engine siezed, smoke Camels, go blind, drink contaminated water or nasty coffee before changing those filters?

I don't care what you do to yourself, just don't piss off the HVAC man or mess with my coffee..